1. Field of the Invention
The present invention generally relates to fixtures for grinding machines, and more particularly to a fixture for grinding machines which prevents ground workpieces from adhering to the fixture.
2. Description of Related Art
Many kinds of workpieces need to be ground to have a desired shape before use. For example, lenses used in digital camera modules are ground to be round to allow their installation into lens barrels. However, when grinding a plurality of workpieces at the same time, fixtures are used to properly secure the workpieces.
Referring to FIG. 8, a typical fixture for securing workpieces includes a first base 50 and a second base 60. The first base 50 is substantially cuboid, a first groove 51 is defined on a surface of the first base 50, and the first groove 51 has a triangular cross section. The second base 60 is also substantially cuboid, a second groove 61 is defined on a surface of the second base 60, and the second groove 61 has a semicircular cross section. A diameter of the semicircular cross section of the second groove 61 is equal to a diameter of ground workpieces.
When a whole piece of material such as glass (not shown) is cut to be a plurality of rectangular workpieces (not shown), then the workpieces are placed into the first groove 51 of the first base 50. Two adjacent sides of each workpiece are engaged with the first groove 51, thus each workpiece is aligned with all other workpieces and pressed close to other workpieces adjacent to itself. Afterwards, some ultraviolet (UV) glue is applied to the workpieces. The ultraviolet glue dries after being irradiated with ultraviolet radiation, thus all workpieces are secured in the first base 50 and form a quadrilateral prism. Two side faces of the quadrilateral prism are exposed from the first groove 51 and the other two face sides of the quadrilateral prism are engaged with the first groove 51. In this way, the ultraviolet glue prevents the workpieces from moving when the workpieces are being ground. A grinding wheel (not shown) is used to grind the two side faces exposed through the first groove 51, thus half of the quadrilateral prism is ground to have a semicircular cross section. In this way, each workpiece is ground to have a first portion and a second portion, the first portion is triangular and the second portion is semicircular whose bottom matches (i.e., is shaped so as to conform to) with the bottom of the first portion. The second portion is exposed through the first groove 51, and the first portion is engaged with the first groove 51.
After grinding the first side, the dried ultraviolet glue is dissolved by water or other kinds of solvent. The second base 60 covers the first base 50, the second portion of each workpiece is engaged with the second groove 61. The first base 50 and the second base 60 are turned together, the first base 50 is removed, and all the workpieces are transferred to the second groove 61 of the second base 60. In this way, the first portion of each workpiece is exposed through the second groove 61. The workpieces are secured in the second groove 61 in a similar way to that in which the workpieces are secured in the first groove 51 and thus form a column. The column includes a cylinder portion and a prism portion, the prism portion of the first prism is exposed through the second groove 61 and the cylinder portion is engaged with the second groove 61. The grinding wheel is used to grind the prism portion, thus the prism portion is also ground to have a semicircular portion. In this way, the column is ground to be a cylinder, and each workpiece is ground to have a round shape.
However, when the dried ultraviolet glue is dissolved for moving the workpieces from the first base 50 into the second base 60, a little ultraviolet glue is likely to remain on the first base 50, particularly in the first groove 51. Therefore, some workpieces are likely to remain attached to the first base 50 by remaining ultraviolet glue when the first base 50 is turned. Placing these workpieces into the second base 60 and adjusting each of the workpieces to sit in a proper position requires much additional work, thus efficiency of cylindrical grinding is decreased. Additionally, if the number of the workpieces placed into the first groove 51 is too large, the quadrilateral prism formed by the workpieces may be too long, and the quadrilateral prism may become distorted when it is ground or turned, and some workpieces may be damaged.
Therefore, a new fixture for grinding machines is desired in order to overcome the above-described shortcomings.